Jumbo cruise ships welcomed aboard luxe amenities and attractions years ago. But these days it's not just the big boats that have spas and art history lectures. Small and midsize ships carrying fewer than 700 people now keep passengers entertained with theme excursions, driving ranges, and menus devised by celebrity chefs (not to mention DVD libraries and bathrooms stocked with designer soap). From the newest fleet at sea, we chose six of our favorite ships—including one large liner that does it better than most.

CRYSTAL SERENITY 1,080 passengers; 866-446-6625; www.crystalcruises.com
THE BRIEF A megaliner with no shortage of diversions for its mostly-over-45 guests: seven restaurants, an art gallery, library, casino, and 8,000-square-foot spa.
WHERE IT GOES The Caribbean, Australia, the South Pacific, and Asia. An 11-day trip around the Mediterranean with former ambassador Richard Peck starts at $3,700.
WHAT'S GREAT The service is fantastic—in the Nobu sushi bar, air-conditioned tenders, and Frette-stocked penthouse staterooms with butlers and flat-screen TVs.
WHAT'S NOT Because of its girth, the Serenity must use tenders to visit small ports, a hindrance for those who like more private and spontaneous outings.

MINERVA II 600 passengers; 877-800-7926; www.swanhellenic.com
THE BRIEF Cruises for the Mind is the motto of this floating English country-house hotel, which takes pride in its excursions to offbeat ports led by expert guides.
WHERE IT GOES Eight-to-16-day trips to Africa, Asia, the Mediterranean, and Northern Europe. A two-week Falkland Islands cruise with a war historian starts at $5,300.
WHAT'S GREAT Amenities include lectures by diplomats, historians, and ornithologists, a huge library, and theme junkets (say, Greek drama at an ancient amphitheater).
WHAT'S NOT The staterooms are small for a ship this size. The majority of rooms are no more than about 200 square feet.

ORION 106 passengers; 800-257-5767; www.traveldynamicsinternational.com
THE BRIEF An intrepid vessel with an ice-strengthened hull and Trussardi toiletries, the Orion is for those who love adventure and pampering in equal measure.
WHERE IT GOES Both wild and tame ports of call, from the Arctic to Chicago, over 7 to 32 days. A 10-day Antarctica trip with a team of geologists begins at $6,000.
WHAT'S GREAT This is serious adventure. Small-group excursions visit places big boats can't, and often on Zodiacs. You'll actually use the boot-washing station.
WHAT'S NOT Orion's size and its daring expeditions represent a tradeoff—one dining room, no balconies, and a marina in lieu of a pool.

SEA CLOUD II 94 passengers; 888-732-2568; www.seacloud.com; www.arrangementsabroad.com
THE BRIEF To embark on this three-masted windjammer is to enter the glamorous, bygone days of sailing. There's even a brass bell to summon you to dinner.
WHERE IT GOES Northern Europe, the Med, and the Caribbean over 8 to 14 days. Eleven days around Iberia with a Metropolitan Museum lecturer starts at $5,250.
WHAT'S GREAT The Sea Cloud's outings are among the most imaginative, incorporating private visits to museums, gardens, and golf courses.
WHAT'S NOT The ship is usually chartered by private groups, so individual booking, though available, can be difficult to arrange.

SEVEN SEAS VOYAGER 700 passengers; 800-285-1835; www.rssc.com
THE BRIEF Traditional luxury on every deck: All rooms are suites with balconies, Le Cordon Bleu has a restaurant on board, and the Carita spa is strictly upper-deck.
WHERE IT GOES The Caribbean, the Baltic, and New Zealand on 8-to-109-day trips. A 10-day Mediterranean cruise with Robert MacNeil and Jim Lehrer begins at $4,500.
WHAT'S GREAT The rooms are some of the chicest at sea, and the themes are sophisticated: opera cruises with a Met diva and excursions like "Historic Jewish Dublin."
WHAT'S NOT The conspicuous luxury can sometimes border on fussy. In two of the five dining rooms, reservations are required and formal dress codes are enforced.

SILVER WHISPER 382 passengers; 800-722-9955; www.silversea.com
THE BRIEF This is a middle-weight cruiser with heavyweight amenities—a golf pro, Mandara Spa, Davidoff Humidor club, and a boutique selling Bulgari and Piaget.
WHERE IT GOES South America, the Med, and Northern Europe over 6 to 16 days. Twelve days on the U.S. Atlantic Coast with former astronaut Wally Schirra starts at $5,450.
WHAT'S GREAT Passengers can customize their itineraries, hopping off and on at most ports. Excursions are plentiful (12 different outings for two days in St. Petersburg).
WHAT'S NOT It's a small quibble, we know, but not all staterooms have balconies.